Portable traffic control systems particularly suited to controlling traffic in work areas have been disclosed (e.g., Moe, U.S. Pat. No. 3,867,718; Terrill, U.S. Pat. No. 2,829,362). Normally, the systems are used on roads that have two traffic lanes, each for traffic in a different direction. When repair work is being performed on one lane of the road, however, the traffic in both directions must use the other lane. The control systems employ traffic lights at each end of the traffic lane, alternately presenting a go signal first to traffic from one direction and then to traffic from the other direction. The signals are not only viewable by oncoming traffic but also by an operator standing between the display units.
It would be desirable, however, to have improved traffic control systems, for example, one having a warning device that is activated by the vehicle of a driver who ignores or does not notice a stop light. It would also be desirable to have a system that uses simplified control circuits with fewer moving parts so as to minimize repair costs for the circuits. Furthermore, it would be preferable that neither red nor green lights on the back side of a display unit be used to convey information to a person behind that display unit about the status of the traffic lights on its front side, since such lights might prove confusing to drivers who are supposed to respond to the front traffic lights on the other display unit.